Outside groups poured $12 million into the Pennsylvania 18th Congressional District race ahead of Tuesday’s special election, with the vast majority of that money coming from conservative groups to boost the GOP candidate, Rick Saccone.

Conservative super PACs and party committees spent $10.7 million to support Saccone or oppose Conor Lamb, the Democrat. In comparison, Democratic groups spent $2 million in support of Lamb or opposing Saccone, Federal Election Commission records filed Monday night show.

Four groups spent more than $1 million: the National Republican Congressional Committee ($3.5 million), the Congressional Leadership Fund ($3.4 million), the Republican National Committee ($1.3 million) and America First Action ($1.1 million). The NRCC is in the lead among groups spending money on advertisements and other electioneering. On the Democrats’ side, the Democratic Congressional Campaign Committee spent just $312,500, filings show.

Republican-leaning outside groups made up for lackluster fundraising by Saccone, whose campaign raised roughly $917,892, compared to about $3.9 million raised by Lamb, according to the filings.

The amounts spent by GOP groups to defeat Lamb are particularly notable, given that the southwestern Pittsburgh-area district is in the heart of Trump country, where the real estate magnate won by 20 points in the 2016 presidential election. Moreover, the district will no longer exist in its current form come November, after the map of Pennsylvania districts is redrawn.

The combined amount spent by outside groups in Pennsylvania amounts to less than half of the $30 million spent in a Georgia special congressional election in 2017. But with both parties looking to Pennsylvania as a test of how their parties will do in the 2018 midterms, outside spending on the race reflects how intensely GOP groups are raising and spending money to hold on to the majority in both chambers of Congress. The party with the White House typically loses seats in the midterms.

Among the groups that spent money on the election since March 10 are the Progressive Turnout Project, the AFL-CIO-backed group Working America, MoveOn.org, the RNC, the Congressional Leadership Fund and the National Rifle Association.